Methods for welding components of battery modules

Abstract

The present invention disclosure relates to a method of welding a tab to a terminal of an electrical cell using an infra-red laser welding system. A first surface of the tab is placed in contact with the terminal of the electrical cell, and an infra-red laser is directed through at least one lens towards a second surface of the tab opposite the first surface. The laser welding system is controlled to produce a weld by directing the beam to follow a predetermined path. During welding, the beam is focussed in a plane between the first surface and the lens. In some embodiments, the beam may be focussed between the second surface and the lens. Advantageously, focussing the beam in this way has been found to reduce undesirable phenomena such as spatter and to produce more reliable welds than prior art methods.

1 . A method of welding a tab to a terminal of an electrical cell using an infra-red laser welding system, wherein the tab has a first surface and a second surface opposite the first surface, the method comprising:
 placing the first surface of the tab in contact with the terminal of the electrical cell; and   directing a laser through at least one lens towards the second surface of the tab; and   welding the tab to the terminal by controlling the infra-red laser welding system to produce a weld, wherein the producing the weld comprises directing a laser beam to follow a predetermined path of the weld,   wherein the laser beam is focussed in a plane between the first surface and the at least one lens.   
     
     
         2 . The method as claimed in  claim 1 , wherein the laser is focussed in a plane between the second surface and the lens, wherein the plane is 0-1 mm away from the second surface. 
     
     
         3 . The method as claimed in  claim 1 , wherein the laser beam has a focussed spot size of 10-50 microns. 
     
     
         4 . The method as claimed in  claim 1 , wherein the infra-red laser welding system is arranged to control the laser beam to oscillate about a centreline of the predetermined path, wherein the oscillations comprise a first component in a direction parallel to the predetermined path and a second component in a direction normal to the predetermined path. 
     
     
         5 . The method as claimed in  claim 1 , wherein the infra-red laser welding system comprises one or more mirrors arranged to move to direct the laser beam, wherein at least one of the one or more mirrors is arranged to move at a speed sufficient to cause a position of the beam on the tab to move at 100-200 mm/s. 
     
     
         6 . The method as claimed in  claim 1 , wherein time taken to produce the weld is 80 milliseconds or less. 
     
     
         7 . The method as claimed in  claim 1 , wherein the terminal is a steel terminal. 
     
     
         8 . The method as claimed in  claim 1 , wherein the tab comprises copper. 
     
     
         9 . The method as claimed in  claim 1 , wherein the laser beam has a power of 500-1000 W. 
     
     
         10 . The method as claimed in  claim 1 , wherein an inert atmosphere is provided at least in a vicinity of the tab and the terminal during the welding of the tab to the terminal. 
     
     
         11 . The method as claimed in  claim 1 , further comprising measuring a position of the tab. 
     
     
         12 . A method of mechanically and electrically connecting a busbar component to a plurality of cells, wherein the busbar assembly comprises a plurality of tabs, the method comprising welding each of the tabs to one or more of the cells, according to the method as claimed in  claim 1 ; 
       wherein the method comprises:
 positioning each of the tabs in contact with one or more of the terminals; 
 positioning the scanning head at a first position relative to the tabs; 
 welding a first group of tabs to the respective terminals by moving the plurality of mirrors to sequentially direct the laser beam towards each of the tabs in the first group, to produce a first group of welds, wherein the scanning head is held at the first position during the production of the first group of welds; 
 positioning the scanning head at a second position relative to the tabs; and 
 welding a second group of tabs to the respective terminals by moving the plurality of mirrors to sequentially direct the laser beam towards each of the tabs in the second group, to produce a second group of welds, wherein the scanning head is held at the second position during the production of the second group of welds. 
 
     
     
         13 . A battery module comprising the busbar component mechanically and electrically connected to a plurality of cylindrical cells according to the method as claimed in  claim 12 . 
     
     
         14 . A battery pack comprising the battery module as claimed in  claim 13 . 
     
     
         15 . A vehicle comprising the battery module as claimed in  claim 13 . 
     
     
         16 . A vehicle comprising the battery pack as claimed in  claim 14 . 
     
     
         17 . The method as claimed in  claim 4 , wherein the oscillations have an amplitude of 0.1-0.5 mm, optionally 0.2-0.4 mm. 
     
     
         18 . The method as claimed in  claim 4 , wherein a frequency of the oscillations is 300-700 Hz. 
     
     
         19 . The method as claimed in  claim 8 , wherein the copper is plated with nickel. 
     
     
         20 . The method as claimed in  claim 12 , wherein the infra-red laser welding system comprises a welding laser and a scanning head comprising a plurality of movable mirrors arranged to direct a laser beam produced by the welding laser.